Burn patient resuscitation system

ABSTRACT

A system for operating a semi-closed loop and/or a closed loop resuscitation of a burn patient in view of patient information and other physiological data gathered by the system. The system in at least one embodiment includes an urine sensor, an infusion pump and a processor that controls the operation of the infusion pump at least in part from a signal received from the urine sensor.

This application is a continuation application of U.S. patentapplication Ser. No. 12/977,609, filed on Dec. 23, 2010, which is adivisional application of U.S. patent application Ser. No. 12/076,554,field on Mar. 19, 2008, which claims the benefit of U.S. provisionalapplication Ser. No. 60/895,670, filed on Mar. 19, 2007 entitledApproaches to Improving Treatment of Burn Patients. These applicationsare hereby incorporated by reference.

The U.S. Government in addition to any other rights it may have throughat least one inventor has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of award numberN00014-03-1-0363 awarded by the Office of Naval Research, Department ofDefense.

I. FIELD OF THE INVENTION

This invention relates to a semi-closed loop or closed loop system andmethod for burn patient resuscitation.

II. BACKGROUND OF THE INVENTION

Effective resuscitation of burn injuries is critical for lowering boththe mortality and morbidity rates of burn patients. Both treatment andrehabilitation of burn injuries requires a large economic investment byhospitals in terms of cost and long term intensive care requirements forpatients with severe and/or large percentage body burns. It is notuncommon that a normal size adult will receive over 30 liters of fluidwhile having urinary output (or urine output) totaling less than 2liters, which results in a gain of about 60 pounds from the fluidretention in the body resulting from, for example, capillary leakage inresponse to the injury.

Each year approximately 45,000 adults and 15,000 children requirehospitalization due to burn injury with 5,000 dying due to the severityor complications resulting from their injuries. For the militarypopulation, injury patterns due to current conflicts may include bothtraumatic and burn injuries that necessitate immediate treatment.Furthermore, recent studies have shown that over resuscitation of burninjury is not uncommon, resulting in significant iatrogeniccomplications.

Critical to survival are the initial 48 hours of post-burnresuscitation; however, this time period is extended in situations wherethe patient takes a long time for care and eventual transport such asoccurs when brining burned soldiers from the Iraq theater to the U.S.Army Institute of Surgical Research (USAISR) burn unit at Fort SamHouston, Tex. During this phase, patients require prompt initiation offluid therapy, and around-the-clock care by experienced burn surgeonsand intensivists. However, advanced burn care expertise is not found inmost hospitals, and the care outside of burn centers can lead toincrease morbidity from infusing too much fluid. This limitationincludes receiving centers, whether they are civilian emergency rooms,forward military facilities or ad hoc medical facilities for masscasualty. Because acute burn care is particularly labor intensive, burninjuries sustained in mass casualties can quickly overwhelm even thebest hospitals and burn centers. Clearly, there is a need to reduce theworkload of advanced burn centers and to impart burn expertise to lessspecialized medical facilities.

The pathophysiologic response to large thermal injuries (≧30% of totalbody surface area [TBSA]) is characterized by substantial plasmaextravasation and general edema formation, leading to intravascularvolume depletion and burn shock. Delayed or inadequate fluidresuscitation is associated with increased morbidity and mortality.Initial treatment currently consists of isotonic crystalloid infusionbased on a regimen that is directed towards volume replenishment toobtain cardiovascular stabilization and maintain adequate renalfunction. However, such treatment is only partially effective due to anarray of circulatory mediators and sustained fluid extravasations intothe extravascular space.

a. Current Resuscitation Regimens

Defining the best solutions, infusion rates, and volume requirements forresuscitation of burn injury has been an ongoing research focus for thelast 100 years. Several formulas have been developed to guide the careprovider with a predicted infusion volume for the first 24 hours andwith a specific initial infusion rate based on the size of the burninjury and patient weight. Infusion rates are adjusted hourly, based onthe urinary output (UO) of the patient during the last measured period.The most common contemporary infusion formulas are the Brooke formula (2ml/kg per % TBSA for 24 hours) and the Parkland formula (4 ml/kg per %TBSA for 24 hours). Fluids are periodically adjusted to maintain anadequate urinary output, within a predetermined target range. Therationale for using urinary output as the target endpoint to adjustfluid therapy is that if urinary output is normal then glomerularfiltration rate, renal blood flow, and cardiac output are likely to beadequate. Target values are based on ranges determined by age (adult orpediatric), patient weight, and sometimes other factors that contributeto normal renal output. Adult target values are 0.5-1.0 ml/kg per houror 30-50 ml/hr. Pediatric patients often require larger volumes due togreater insensible losses, and have a formula with a higher targeturinary output of 1.0-2.0 ml/kg per hr. Maintaining urinary outputtargets is expected to normalize renal function, while avoiding excessor inadequate fluid infusion that may lead to an increase incomplications or mortality. But recent reviews have suggested that thisapproach frequently leads to severe over-resuscitation, with many burnunits administering mean volumes larger than the Parklandrecommendation.

The current standard of care for patients receiving burn resuscitationis paper charts that include a flow sheet similar to that illustrated inFIG. 1A. In some situations where electronic charting is used, themonitors will provide data to the electronic charting system asillustrated in FIG. 1B, which is only a slight improvement over the flowsheet since there is no analysis of the data.

To evaluate contemporary methods of burn resuscitation, a meta-analysisof the last 26 years of burn resuscitation was conducted. A search ofMedline for all clinical burn studies in which fluid resuscitation wasguided by the Brooke or Parkland formula with adjustment in infusionrates to restore and maintain target urinary output was done. Data from31 studies, which included 40 groups and 1,498 patients was extracted.FIGS. 2A and 2B show the total 24-hr volumes infused and the meanurinary outputs, respectively. Mean percentage of total body surfacearea (% TBSA) was 45±2% and mean fluid intakes were 5.1±1.3 mL/kg per %TBSA, with mean 24-hr urinary outputs of 1.1±0.4 mL/hr per kg. Allstudies reported mean volume administration exceeding the Brooke formulaand 86% of studies reported mean values above the Parkland formula. Ingeneral, patients are resuscitated to achieve levels of urinary outputthat are at or above the high end of target level. However, most of theburn centers infused sufficient lactated Ringer's solution (LR) toinduce mean 24-hour urinary outputs exceeding 1.0 mL/kg. The primaryconclusions from the meta-analysis are: (1) total volumes infusedtypically exceed the Parkland formula and Advanced Burn Life Support(ABLS) guidelines, and (2) urinary outputs tend to be on the high sideof ABLS guidelines.

The meta-analysis did not determine if burn centers are infusing morefluid than is optimal or if the Brooke and Parkland burn formulasspecify inadequate volumes. A meta-analysis based on summary statisticsof individual studies has limited power to determine relationshipsbetween fluid volumes and outcomes. Detailed individual patient data areneeded to accurately determine the impact of fluid therapy on outcomes.Individual patient data is required to statistically correlate outcomeswith total volumes infused and net volume retained (in minus out).Hourly data on infusion rates, urinary output and net volume (edema) isneeded to fully define the relationships between volume therapy andurinary output in burn patients.

Reduced survival and more often increased morbidity are linked tosub-optimal resuscitation. But it is unknown how many patients areharmed by under- and over-resuscitation. From the meta-analysis, casereports, and clinical experience we know that individual burn expertsresuscitate patients differently and that they usually produce clinicalresults deemed satisfactory. This may speak more to the physiologicalreserves of the patients and the ability of their kidneys to compensatefor over-resuscitation than it does to our medical knowledge orexpertise. A quip often used by intensivists is “the dumbest kidneyknows more than the smartest intern.” Patients have effectivecompensatory mechanisms that can often compensate for a wide range ofinfused volumes. “Successful clinical results,” however, are notnecessarily equivalent to optimal outcomes.

b. Fluid Creep

The need for large volume therapy for burn shock was identified in 1968by Charles Baxter, who showed that successful resuscitation could beaccomplished with a “Parkland formula” of 4-ml/kg per % TBSA of lactatedRinger's solution in the first 24 hours of care. Baxter C R, et al.,Physiological response to crystalloid resuscitation of severe burns,Annals of the New York Academy of Sciences, 1968, vol. 150, pp. 874-894.Prior to that time, fluid therapy was largely performed with plasma andalbumin solutions at lower volume totals. Subsequently, Pruitt et al.provided an alternate “Brooke formula” of 2-ml/kg per % TBSA. Pruitt B AJr., Fluid and electrolyte replacement in the burned patient, Surg ClinN Am., 1978, vol. 48, pp. 1291-1312. The Advanced Burn Care Life Support(ABLS) guidelines established by the American Burn Association acceptedthese formulas and recommend a 2-4 mL/kg per % TBSA range of total fluidvolumes for the first 24 hours, with the infusion rate adjusted tomaintain a urinary output of between 0.5 mL/kg and 1.0 mL/kg per hr orabout 30-50 ml/hr. American Burn Association, Advanced Burn Life SupportCourse (ABLS), Instructor's Manual, 2001. Nevertheless, burn centersroutinely administer 25-50% more fluid than the Parkland formularecommends, and more than half the fluid is given within the first 8hours. In clinical settings, physicians may accept high urinary outputswithout decreasing infusion rates and more diligently increase infusionrates when urinary output is low. This viewpoint is supported bymeta-analysis, which showed that mean urinary outputs and infusedvolumes were typically above ABLS guidelines.

The term “fluid creep” was first used by Pruitt to describe theincreased volume of fluid that appears to be administered by burncenters in the first 24-48 post-burn hours. The morbidities associatedwith fluid overload include pulmonary edema and impaired gas exchange,abdominal compartment and intestinal ischemia syndromes, delayed woundhealing, increased incidents of infection and sepsis, and multi-organfailure. Data supports benefits of reducing total infused volumes.Recently, perioperative and ICU trials of restricted fluid therapyshowed improved outcomes. Brandstrup B et al., Effects of intravenousfluid restriction on postoperative complications: comparison of twoperioperative fluid regimens: a randomized assessor-blinded multicentertrial, Annals of Surgery, 2003, vol. 238, pp. 641-648. Less net fluidaccumulation has been associated with better outcomes in large burnstreated with lactated Ringer's solution (LR). Cancio L C, PredictingIncreased Fluid Requirements During the Resuscitation of ThermallyInjured Patients, The Journal of Trauma, February 2004, vol. 56, No. 2,pp. 404-413. However, the correlation between increased survival andreduced fluid also reflects that the injury level correlates morbidityand mortality, and that more severely burned patients require morefluid.

Taken together the above findings suggest that optimal fluidresuscitation may be achieved by minimizing fluid accumulation, whilemaintaining adequate urinary output and cardiac output. However, theclinical consequences of more tightly controlled fluid therapy andurinary output to fall within established guidelines with less hourlyvariations are unknown.

c. Fluid Therapy Using Closed Loop Control

The concept of closed loop control is well established for industrialapplications and its potential application to medicine has beenextensively reviewed, although it has had limited utilization. Abbod MF, Survey on the use of smart and adaptive engineering systems inmedicine, Artificial Intelligence in Medicine, 2002, vol. 26, pp.179-209; Westenskow D R, Microprocessors in intensive care medicine,Medical Instrumentation, November-December 1980, vol. 14, no. 6, pp.311-313. There have been clinical trials demonstrating effective closedloop control of nitroprusside infusion for postoperative blood pressureregulation in cardiac patients. Ying H, Fuzzy control of mean arterialpressure in postsurgical patients with sodium nitroprusside infusion,IEEE Transactions on Biomedical Engineering, 1992, vol. 39, pp.1060-1070. Closed loop control of ventilators and delivery ofanesthetics have evolved into commercially viable products. Brunner J X,Principles and history of closed-loop controlled ventilation,Respiratory Care Clinics of North America, 2001, vol. 7, pp. 341-362,vii; Wysocki M et al., Closed-loop ventilation: an emerging standard ofcare?, Critical Care Clinics, 2007, vol. 23, pp. 223-240, ix.Experimentally, closed loop fluid resuscitation has been used fortreatment of hemorrhaged sheep using blood pressure, cardiac output, andtissue oxygen as endpoints. Chaisson N F et al., Near-InfraredSpectroscopy-Guided Closed-Loop Resuscitation of Hemorrhage, The Journalof Trauma, 2003, vol. 54, no. 5, pp. S182-S192; Rafie A D et al.,Hypotensive resuscitation of multiple hemorrhages using crystalloid andcolloids, Shock, 2004, vol. 22, pp. 262-269.

Bowman and Westenskow were the first to build a closed loop controller(using a proportional-integral-derivative (PID) algorithm) for fluidresuscitation of burn injury. Bowman et al., “A Microcomputer-BasedFluid Infusion System for the Resuscitation of Burn Patients,” IEEETransactions on Biomedical Engineering, Vol. BM-28, No. 6, June 1981,pp. 475-479. In an era before personal computers were common, they builta specialized microprocessor for their controller. Both intake andurinary output were monitored with drop counters while a roller infusionpump was controlled with the PID algorithm. The PID algorithm was basedon a mathematical model, which had been used to control resuscitation ina small number of dog experiments. They verified accurate monitoring offluid in and urine out, but no control trials were performed in eitheranimals or patients. Several decision trees and mathematical models offluid balance after burn injury have been developed, but none has hadsignificant clinical application. Bert J L et al., Microvascularexchange during burn injury: II. Formulation and validation of amathematical model, Circulatory Shock, 1989, vol. 28, pp. 199-219; BertJ L et al., Microvascular Exchange During Burn Injury: IV. FluidResuscitation Model, Circulatory Shock, 1991, vol. 34, pp. 285-297; RoaL M et al., Analysis of burn injury by digital simulation, BurnsIncluding Thermal Injuries, 1988, vol. 14, pp. 201-209.

An evaluation of individual hourly records of burn patients was done inorder to define a current standard of care for burn resuscitation.Hourly fluid input and urinary output measurements from 20 adult burnpatients were extracted from U.S. Army Institute of Surgical Research(USAISR) and University of Texas Medical Branch (UTMB) burn unitrecords. The data shown in FIG. 3 suggests great variability in urinaryoutputs before and after arrival at these two burn centers. Of 403hourly in-hospital measurements in burn patients, 41% were below theABLS target range of 1.0-2.0 mL/kg and 28% were above.

The principle conclusions from the analysis of these patients and of theliterature meta-analysis are that mean urinary output above targetlevels predominated with infused volumes, even in advanced burn centers,exceeding ABLS guidelines. The tendency for clinicians toover-resuscitate burn patients may be responsible for many recognizedcomplications such as abdominal compartment syndrome, extremitycompartment syndrome, and airway edema requiring intubation, all ofwhich are life- and/or limb-threatening. In particular, abdominalcompartment syndrome was largely unheard before ten years ago, but isnow a serious complication in many burn centers that results almostalways in death.

III. SUMMARY OF THE INVENTION

Effective resuscitation is critical in reducing mortality and morbidityrates of acute burn patients. Specific closed loop system usingcomputer-controlled feedback technology that supplies automatic controlof infusion rates using decision assist guidelines can potentiallyachieve better control of urinary outputs. Because the system canself-adjust based on monitoring inputs, the technology can be pushed toenvironments such as combat zones where burn resuscitation expertise islimited. A closed loop system can also assist in the management of masscasualties, another scenario in which medical expertise is often inshort supply.

The invention in at least one embodiment uses an expectant rate model todetermine infusion rate based on urinary output with the expectant ratemodel based on how patients from a reviewed pool responded toresuscitation with fine-tuning for any one patient done to bring thepatient into a desired urinary output range.

A systematic means for adjusting infusion rate using either decisionassist algorithm or autonomous closed loop control may improve outcomesin patients requiring large volume fluid therapy.

Closed loop resuscitation systems can provide physicians, nurses, andother medical personnel who have limited burn experience a means tooptimize the first 24 to 48 hours of burn care, even in an initial carefacility. Although the invention can be used for more than 48 hours. Inthe prehospital mass casualties environment, or in advanced burn centerssuch systems could be labor saving.

At least one embodiment provides for continuous monitoring andapplication of control algorithms to achieve and maintain urinary outputtarget levels better than human intervention. This critical ability totightly manage fluid balance is due to the closed loop system's abilityto continuously monitor, and rapidly interpret and respond to minutesystemic changes using the application of consistent rules. A closedloop controller can adjust fluid infusions at least as well as typicalclinical burn care teams. This in itself will be useful. Animal studiessuggest that tighter control of urinary output may lower total volumeinfused and total net fluid balance. However, even if such systems yieldoutcomes no better than that of advance burn centers, the technologywould allow expertise to be “exported” to other hospitals and traumacare facilities that do not have expertise or experience in burn care.

The invention in at least one embodiment includes a system for use inresuscitating a patient that operates as a semi-closed loop system, aclosed loop system, or a combination of the two. The system includes aurine sensor; an infusion pump; and a processor connected to said urinesensor and said infusion pump, said processor having means forcalculating an infusion rate based on at least the current infusionrate, the current urinary output, infusion rate model based constants,the patient's weight, the percentage of total body surface area, and aGaussian function centered on a target urinary output, and means forcontrolling operation of said infusion pump based on the calculatedinfusion rate.

The invention in at least one embodiment includes a method forcontrolling the operation of a resuscitation system used to resuscitatea burn patient. The method includes receiving patient data includingpercentage of total body surface area; calculating an initial infusionrate based on at least the patient data; outputting the initial infusionrate to an infusion pump; obtaining a current urinary output from asensor monitoring urinary output; calculating a new infusion rate basedon at least the current infusion rate, the current urinary output, aninfusion rate constant, an urinary constant; and outputting the newinfusion rate to the infusion pump.

The invention in at least one embodiment includes a system for use inresuscitating a patient where the system includes: a urine sensor; aninfusion pump; and a processor connected to the urine sensor and theinfusion pump, the processor having means for calculating an infusionrate using an infusion rate model based on at least a current infusionrate, a current urinary output, and infusion rate model based constants,the new infusion rate is calculated using the following equation

$I_{t} = {I_{t - 1} + {{e(t)} \times \frac{I\; R\; C_{t}}{{UOC}_{t}}}}$where I_(t) is the new infusion rate, I_(t-1) is the last infusion rate,e(t) is the urinary output error between the current urinary output anda target urinary output, IRC_(t) is the infusion rate constant at time tbased on the hours post burn, and UOC_(t) is the urinary constant, andmeans for controlling operation of the infusion pump based on thecalculated infusion rate.

The invention in at least one embodiment includes a system for use inresuscitating a patient where the system includes: a urine sensor; aninfusion pump; a timer; and a processor connected to the urine sensor,the infusion pump, and the timer, the processor having means forcalculating an infusion rate based on at least the current infusionrate, the current urinary output, infusion rate model based constants,the patient's weight, the percentage of total body surface area, and aGaussian function centered on a target urinary output, and means forcontrolling operation of the infusion pump based on the calculatedinfusion rate.

The invention in at least one embodiment includes a system for use inresuscitating a patient where the system includes: a urine sensor; aninfusion pump; receiving means for receiving patient data includingpercentage of total body surface area burned and time since the patientwas burned; first means for calculating an initial infusion rate basedon at least the received patient data; second means for calculating anurinary output error based on a difference between a target urinaryoutput and a current urinary output provided by the urine sensor; thirdmeans for calculating a new infusion rate based on at least thecalculated urinary output error multiplied by a constant calculated inpart based on an exponential function with the input of hours post burnfor the patient with the result being added to the current infusionrate; outputting means for outputting the new infusion rate to theinfusion pump; and a timer for controlling the operation of the secondmeans, the third means and the outputting means.

Given the following enabling description of the drawings, the apparatusshould become evident to a person of ordinary skill in the art.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

In some of the figures in the patent application, certain informationhas been redacted to remove identification of any patients from or hasreplace identifying information with non-descript information in theillustrated interfaces

The present invention is described with reference to the accompanyingdrawings. In the drawings, like reference numbers indicate identical orfunctionally similar elements. The use of cross-hatching and shadingwithin the drawings is not intended as limiting the type of materialsthat may be used to manufacture the invention.

FIGS. 1A and 1B illustrate the current records being used in the burncenters.

FIGS. 2A and 2B depict data regarding fluid infused and urinary outputobtained from a retroactive study.

FIG. 3 illustrates the number of urinary output measurements and wherethey fell along a spectrum from medical records at UTMB and USAISR.

FIGS. 4A-4C depict different functions that are used in at least oneembodiment to determine a new infusion rate.

FIGS. 5A and 5B illustrate one example interface for enteringinformation into the system.

FIG. 5C illustrates another example interface for entering informationinto the system.

FIG. 5D illustrates another example interface for entering informationinto the system.

FIGS. 6-8 illustrate different embodiments for calculating an infusionrate.

FIG. 9 illustrates an exemplary embodiment according to the invention.

FIGS. 10A-10F illustrate different example displays for receiving and/orproviding information to the user

FIGS. 11A and 11B illustrate different alternative embodiments accordingto the invention.

FIGS. 12A-12C illustrate different alternative embodiments according tothe invention relating to problem detection.

FIG. 13 illustrates an embodiment using different aspects of thepreceding embodiments as an example according to the invention.

FIG. 14 illustrates an embodiment using different aspects of thepreceding embodiments as an example according to the invention.

FIGS. 15A-15C illustrates a block diagram of a system according to theinvention.

FIGS. 16A-16E illustrate together with FIGS. 10A and 10B an example setof interfaces according to the invention.

FIG. 17 illustrates an example interface according to the invention.

FIGS. 18-21 depict data supporting the invention.

V. DETAILED DESCRIPTION OF THE DRAWINGS

The invention includes a method for providing controlling the infusionrates of a semi-closed loop system or a closed-loop system to achieve atarget urinary output using model based infusion constants. Urinaryoutput is a surrogate marker for renal blood flow, adequateresuscitation and adequate cardiovascular function, but does not requirean invasive procedure to be able to monitor blood flow to be able tomonitor cardiovascular function. The system was developed based in parton a retrospective analysis of 30 burn patients at the USAISR burn wardthat had greater than 20% TBSA. The retrospective analysis will bediscussed later in this specification.

The invention also includes a system capable of performing and/orimplementing the method, and an example of a system is discussed inconnection with FIGS. 10A-10F and 15A-18. The semi-closed-loop systemand the closed-loop system use a compensation model will make a decisionon the level of titration that can be used in conjunction with a urinemeter (or sensor) to receive urinary output data and an infusion pump toset the infusion rate. In such an arrangement, the system can makeadjustments more frequently than occurs with human oversight. Thefrequency at which sampling can occur in such an arrangement is limitedby the accuracy of the urinary output meter and physiology; however,standard filtering can be used to reduce noise and counteract theselimitations.

A semi-closed loop system is one in which the recommendation for theinfusion rate is provided to the medical staff for their approval (oracceptance) before the infusion rate is used by the system. In at leastone embodiment, upon expiration of a predetermined time limit with noresponse from the medical staff, the recommended infusion rate is usedby the system. In some embodiments, the semi-closed loop system willreceive a different infusion rate from the medical staff then thatrecommended to be used. In contrast, a closed loop system will operateindependent of interaction with the medical staff, although in someembodiments the system will provide information related to theresuscitation to allow for oversight by the medical staff and/or allowfor the medical staff to terminate the resuscitation if needed. Bothsystems are able to utilize the following described method forcontrolling the calculation of the infusion rate that governs aparticular burn resuscitation. In at least one embodiment, the user isable to select whether the system will operate as a semi-closed loopsystem or as a closed loop system.

The recommendations provided by the invention are based at least on theurinary output of the patient, infusion rate given to the patient, andhours post burn (HPB). In some embodiments, the recommendations arebased also on at least one of patient weight and percentage of totalbody surface area (TBSA). In some embodiments, the recommendations arebased also on at least the length of time of a certain physiologicalcondition. An example of a system that can provide the information tothe method is an infusion pump and a flow meter measuring the amount ofurine collected through a catheter.

An example of a base infusion rate calculation that can be used in themethod and by the system is

$\begin{matrix}{I_{t} = {I_{t - 1} + {{e(t)} \times \frac{I\; R\; C_{t}}{{UOC}_{t}}}}} & \left( {1A} \right)\end{matrix}$where I_(t) is the new infusion rate, I_(t-1) is the last infusion rate,e(t) is the urinary output error, IRC_(t) is the infusion rate constantat time t based on the hours post burn, and UOC_(t) is the urinaryconstant. Based on data analysis sampled from clinical records of thirtyburn patients, UOC_(t) is set at 1.211. Equation (1) defines the newinfusion rate based on the mean model values found through recursivestudy of burn resuscitation data. The infusion rate constant and urinaryconstant are model based constants derived from data analysis ofclinical records of burn patients.

Equation (1) can be adjusted to reflect that not all patients have thesame weight and/or total body surface area. As such Equation (1) in atleast one embodiment is modified to include at least one of a weightmodifier (Y_(weight)) or a total body surface area modifier (Y_(tbsa)) sillustrated in Equation (1B) that includes both modifiers:

$\begin{matrix}{I_{t} = {I_{t - 1} + {{e(t)} \times \frac{I\; R\; C_{t}}{{UOC}_{t}} \times Y_{weight} \times Y_{tbsa}}}} & \left( {1B} \right)\end{matrix}$

An example of an equation to provide the modifiers for weight and totalbody surface area is

$\begin{matrix}{Y = {A + \frac{C}{\left( {1 + {T\;{\mathbb{e}}^{- {B{({X - M})}}}}} \right)^{1/T}}}} & (2)\end{matrix}$

FIG. 4A illustrates a graphical representation of a function that can beused for Y_(weight) where the y-axis is the function modification factorand the x-axis is the patient's weight in kilograms. The modificationfactor is in the approximate range of 0.1 to 1.2 with it generallyincreasing with the weight of the patient before substantially levelingoff around 100 kg. The illustrated function is produced by setting Aequal to 0.001, C equal to 1.20, M equal to 93, B equal to 0.2, T equalto 7, and X equals the weight of the patient in kilograms.

FIG. 4B illustrates a graphical representation of a function that can beused for Y_(tbsa) where the y-axis is the function modification factorand the x-axis is the patient's percentage total body surface area. Theillustrated function is produced by setting A equal to 0.001, C equal to1.20, M equal to 33, B equal to 0.2, T equal to 2, and X equals thepercentage of total body surface area. The percentage of total bodysurface area could be manually entered by the user into a % TBSA datafield in an interface and received by the system from, for example, thepatient's electronic medical records. Or an interface similar to what isshown in FIGS. 5A and 5B could be used to assist the user in enteringthe estimated percentage of total body surface area into the system.FIG. 5A illustrates an interface that allows the user to paint 505 overa human representation 510 divided according to the Rule of Nines toshow where the patient is burned and to what extent. Based on thisinformation, the system calculates an estimate for % TBSA and outputsthat estimate 515 as illustrated in FIG. 5B. The interface illustratedin FIG. 5B provides an example of one way the patient's weight 520, timeof injury 525, additional injury information 530 and other informationmight be entered into the system. The illustrated interface in FIG. 5Balso illustrates an icon for obtaining an initial infusion rate 535. Thepercentage total body surface area can also be pulled from an electronicmedical record for the patient or estimated using a Lund-Browder chart.

In a further embodiment, the new infusion rate equation is modified toinclude a Gaussian function. The addition of the Gaussian functionreduces the change to the recommended infusion rate as the patient'surinary output approaches the target urinary output. FIG. 4C illustratesan example of a Gaussian function (G_(UO)) centered on a target urinaryoutput of 40 mL/hr. An example of an equation that replicates thefunction illustrated in FIG. 4C isG=1−Ae ^(−(X−B)) ² ^(/C) ²   (3)where A is set to 1; X is set to the current urinary output; B is set tothe target urinary output, which is 40 mL/hr in this example; and C isset to 5. There are at least two schools of thoughts regarding targeturinary output. One school of thought is that the urinary output shouldbe between 30 mL/hr to 50 mL/hr for a normal sized person. The secondschool of thought is that body weight impacts urinary output, so targetranges need to be normalized for the patient being cared for by themedical staff. For example, the value of B can be adjusted for apediatric patient by selecting a value within the range appropriate forpediatric patients that is determined based on weight such that urinaryoutput is normalized for weight. An alternative is to set the targeturinary output (B) towards the end of the target range, which asdiscussed later in the burn field is 30 mL/hr to 50 mL/hr for adults,furthest from the current output and move the target urinary outputtowards the center as urinary output approaches the target range. Thenew infusion equation (1) becomes

$\begin{matrix}{I_{t} = {I_{t - 1} + {{e(t)} \times \frac{I\; R\; C_{t}}{{UOC}_{t}} \times Y_{weight} \times Y_{tbsa} \times G_{UO}}}} & \left( {1C} \right)\end{matrix}$Alternatively, any mix of the modifiers for the weight, the total bodysurface area, and the Gaussian function may be utilized. These modifiersare examples of infusion modifier values based on the described infusionmodel for burn patients that allow for the infusion rate to take intoaccount additional information other than urinary output and asdiscussed below the level of modification is dependent upon where theparticular characteristics fall in the respective functions.

FIGS. 6 and 7 illustrate two different example embodiments fordetermining infusion rates that may be used in the later describedmethods for providing decision-support for resuscitation. Both examplesmake use of the urinary output, the last infusion rate, and the totalbody surface area in determining a new infusion rate.

FIG. 6 illustrates one example of how to calculate the new infusion rate(I_(t)) based on previously entered patient data including the totalbody surface area (Y_(tbsa)) and the patient's weight (Y_(weight)) andon information generated in the system including the urinary output, thelast infusion rate, and the number of hours post burn. FIG. 5Cillustrates an example of an interface that can be used to enterinformation regarding the patient and to identify different monitors(e.g., urinary output meter and infusion pump) that are providinginformation into the system. The illustrated fields allow for manualentry of the information either as textual information or a selectionusing graphical interfaces to setup the initial information regardingthe patient in the system. Alternatively, as discussed above theinfusion rate equation can take a variety of forms with the common basisfor calculating including the last infusion rate, the current urinaryoutput, and the hours post burn.

FIG. 6 illustrates the method based on the current urinary output,computing an error rate for the urinary output, 605. An example of anequation that can be used for this computation ise(t)=UO _(t) −UO _(target)  (4)where UO_(t) is the current urinary output that is obtained by thesystem and UO_(target) is the target urinary output. The target urinaryoutput in at least one embodiment for use with adults is selected from arange of 30 mL/hr to 50 mL/hr, and in at least one embodiment the targeturinary output is set to 40 mL/hr. As discussed above, the urine targetoutput can be normalized based on the patient's weight. An alternativeis to set the target urinary output towards the end of the target rangefurthest from the current output and move the target urinary outputtowards the center as urinary output approaches the target range.

After the urinary output error (e(t)) is obtained, then a new infusionrate (I_(t)) is calculated, 615, using one of the above-describedequations and their discussed alternatives. In this embodiment example,the infusion rate constant at time t is determined as follows:IRC _(t)=3.8975e ^((5.828−0.035HPB))  (5)where HPB is the hours post burn and e is the exponent function. Avariety of equations that produce a decaying level for the infusion asthe resuscitation progresses may be used for determining the infusionrate constant.

If a more frequent sampling of the urinary output occurs, then the aboveequations can be adjusted to reflect the increase in sampling, forexample, the infusion rate constant (IRC_(t)) and the urinary outputerror (e(t)) with the example of 40 mL/hr would need to beproportionally adjusted from the current one hour sampling period. Theseexample equations are set for sampling at 1 hour increments.

FIG. 7 illustrates an alternative method for calculating the newinfusion rate that sets IRC_(t) to a constant value for each of threephases. As occurs in FIG. 6, the urinary output error rate is obtained,605. An infusion rate equation is selected based on the number of hourspost burn, 710. The system can either run a timer to track the timesince the burn occurred or use a comparison between the current timewith time entered for the burn occurring. The selected infusion rateequation (or infusion rate function) is used to calculate the newinfusion rate, 615.

Three phrases were selected based on empirical data obtained fromregression studies of burn patient resuscitation. An example of thethree phases is: Phase I—hours 0-13, Phase II—hours 14-33, and PhaseIII—34 hours and beyond. Typically during Phase I, the patient requiresa massive infusion of fluid and will have instability in terms ofcardiovascular function and variability in relationships between infusedfluid and urinary output. Typically during Phase III, the patient willreceive less fluid infusion and will become stable with the net fluidbetween infused fluid and urinary output decreases and/or becomessubstantially stable. Using these three phase ranges, the IRC_(t)constant is set as follows:

-   -   Phase I: −36.53 mL    -   Phase II: −21.55 mL    -   Phase III: −11.57 mL        which represent the average rate of infusion change per each        hour of each phase. The three I_(t) functions based on        equation (1) become

$\begin{matrix}{{Phase}\mspace{14mu} I} & \; \\{I_{t} = {I_{t - 1} + {{e(t)} \times \frac{- 36.53}{1.211}}}} & \left( {1D} \right) \\{{Phase}\mspace{14mu}{II}} & \; \\{I_{t} = {I_{t - 1} + {{e(t)} \times \frac{- 21.55}{1.211}}}} & \left( {1E} \right) \\{{Phase}\mspace{14mu}{III}} & \; \\{I_{t} = {I_{t - 1} + {{e(t)} \times \frac{- 11.57}{1.211}}}} & \left( {1F} \right)\end{matrix}$

Either of the above methods illustrated in FIGS. 6 and 7 may furtherinclude setting an absolute minimum infusion rate (I_(min)) such as 125mL/hr. FIG. 8 illustrates determining whether the new infusion rate(I_(t)) is less than a predetermined minimum infusion rate (I_(min)),820. If the new infusion rate (I_(t)) is low, than setting the infusionrate (I_(t)) equal to a minimum infusion rate, 825.

FIG. 9 illustrates an embodiment for providing a recommendationregarding a new infusion rate. As illustrated, the method begins withthe system receiving patient data, 905. The patient data receivedincludes, for example, hours since the burn injury, the current urinaryoutput, the current infusion rate, the patient's weight, and thepatient's total body surface area. Additional examples of patient datainclude total urinary output prior to arrival 540 and total infusionprior to arrival 545 as illustrated, for example, in FIG. 5C. In someembodiments, at least a portion of this information is pulled from thepatient's medical record. The minimum amount of patient data is dictatedby the infusion rate calculation used by the method as described aboveand illustrated in FIGS. 6-8. The processor calculates an infusion rate,910, based on the received data or current data when adjusting theinfusion rate, 910. The infusion rate is determined using one of themethods described in connection to FIGS. 6-8.

The processor outputs the infusion rate, 915. Examples of outputting theinfusion rate include, for example, displaying the infusion rate,printing the infusion rate to paper, storing the infusion rate, sendinga notification to medical staff, sending the infusion rate to asemi-closed-loop or closed-loop system to control operation of aninfusion pump, sending a control signal to an infusion pump to adjustthe infusion rate, and a combination of these. In a semi-closed loopsystem, outputting includes, for example, displaying the infusion ratefor acceptance by the medical staff before sending a signal to aninfusion pump of the value to a controller. Displaying the infusion rateincludes, for example, providing the current recommended infusion rateas a number 1005 as illustrated in FIG. 10A and graphically versus timeas illustrated in FIG. 10B-10D. FIG. 10A illustrates a display thatshows the patient information 1010, the current infusion rate selectedby the medical staff (e.g., the doctor) 1015, the urinary output 1020,and the recommendation for the new infusion rate 1005. FIG. 10Aillustrates a situation where the medical staff has chosen to ignore therecommendation for the new infusion rate. In at least one embodiment,the system will require that a reason be provided for a change from therecommended infusion rate to document the care provided to the patient.FIGS. 10B-10D illustrate an interface that shows the infusion rate 1015Aover the last few hours, also illustrated is a series of dots 1005Arepresenting the recommend level of fluid infusion compared to theactual levels of fluid infusion provided to the patient. FIG. 10B wascreated based on a retrospective analysis of the full clinical record ofa patient cared for at a top burn center and suggests that the inventionwill be more beneficial than current resuscitation approaches used inthe medical field. FIGS. 10D and 10E illustrate an example interfacethat shows the cumulative infusion volume 1015C provided to the patientsince the burn occurred. FIG. 10E also illustrates displaying infusionlimits 1025A, 1025B, 1025C based on the patient's weight and percentagetotal body surface area (although in some embodiments, the percentagetotal body surface area is omitted) to provide guidelines to avoidabdomen pressure buildup and thus reduce the risk of morbidity.

The processor in at least one embodiment waits for a period of timebefore calculating a new infusion rate, 920. A period of time is allowedto elapse such as 5 minutes, 10 minutes, 15 minutes, 30 minutes, or 60minutes although over periods of time could be used in a range of 1minute to 90 minutes depending upon, for example, whether the output isbeing provided to medical staff in a semi-closed loop system or aclosed-loop system. In a closed-loop system, the wait time is preferablyunder 20 minutes to allow for quicker response and adjustment of theinfusion rate to reflect changes in the patient. In contrast, thesemi-closed loop system will have wait times that are longer to lessenthe impact upon the medical staff needing to interact with the system.In at least one embodiment for the semi-closed loop system, the usersets the wait time to reflect the staffing situation and other factorsbeyond the control of the semi-closed loop system. Alternatively, thewait delay for the first time through the method may be shorter toprovide an initial urinary output and to allow for the infusion rate tobe adjusted sooner to reflect the patient's condition. When the methodis repeated again, the length of the delay is determined based on thecurrent condition of the patient. Less frequent checks are desirable tolessen the impact on the medical staff in terms of monitoring thepatient, although the frequency should be at least once per hour. In atleast one embodiment, the wait time is adjusted based on whether certainurinary outputs conditions have been met. For example, if any of theurinary output determinations are positive, then the method can set thewait time to a shorten time period.

After waiting for a period of time, the processor obtains the currenturinary output, 925. Different ways to obtain the urinary outputinclude, for example, a device measuring the urine volume, a drop ratesensor measuring the amount of fluid passing from the urine catheter, ora manual entry of volume from a visual inspection by the medical staff.The urinary output can be based on a variety of approaches thatprorate/extrapolate the flow to the appropriate length of time such asone hour. The urinary output can be based on, for example, a running oneminute average for the last five minutes extrapolated to an hour flowrate, the extrapolated flow based on the last five or ten minutes to anhour flow rate, and the captured flow for the last sampling periodadjusted to an hour flow rate. This will allow a modification of thehourly model and allow the decision assist method to be used as part ofa closed-loop system that adjusts the infusion rate, for example, everyfive minutes. In an embodiment that is implemented, the processorreceives a urinary output as a volume amount that is converted into aflow rate based on the difference in volume since the last urinaryoutput reading divided by the time difference, which in some embodimentsis normalized to a one hour period or other wait delay period.

An alternative method includes displaying information regarding theurinary output of the patient in addition to infusion rate informationas illustrated, for example, in FIGS. 10A-10E. FIG. 10A illustrates theurinary output as a number 1020 in mL/hr. FIGS. 10B-10E illustrate theinformation being provided over time 1020A to assist the medical staffin treating the patient and potentially noticing trends that may beoccurring. FIGS. 10C, 10E, and 10F illustrate the inclusion of a targetrange for urinary output 1030. FIG. 10D illustrates the cumulative totalfor urinary output 1020C and a cumulative net fluid retention 1035C.Alternatively, the net fluid balance may be presented to the medicalstaff so that trends can be acted upon if needed. The timing and extentof the response (if any) exhibited by the patient provides confirmationas to whether the current fluid therapy approach is working and whetherthe medical staff may need to try a different treatment approach.

In at least one embodiment, the user interface for the system includes,for example, a graphical element, button, or other similar mechanism forthe medical staff to mark when a physiologic “challenge” is given to thepatient. A benefit to displaying the infusion rate versus time 1015Aalong with the urinary output versus time 1020A is that when a bolus orsome other physiologic “challenge” is delivered to the patient to testthe patient's volume responsiveness, then that information can bedetermined by visual inspection of the graphical presentation. In atleast one other embodiment, the magnitude of the urinary output responseand the delay between the challenge and the urinary output response isdetermined by the system based on the time course of the urinary output.The method takes this information into account to assess if thepatient's urinary output is responding to the infused volume. When apatient does not respond well, a larger bolus or higher infusion ratecan be recommended as part of the method. However, there is an upperlimit of infusion rate that can be safely utilized. Thus, when a patientis a non-responder the medical staff is alerted for consideration ofother techniques, such as cardiovascular drugs.

An alternative embodiment for setting an initial infusion rate is to useeither the Brooke or Parkland formulas. Another alternative embodimentis to use a predetermined infusion rate as the initial infusion rate toattempt to expedite obtaining urinary output in the target range. Afurther alternative embodiment uses the Rule of Tens to set the initialinfusion rate. For example, for a patient who ways 80 kg or less thepercentage of total body surface area is multiplied by 10 to set theinfusion rate in mL/hr; and when the patient's weight exceeds 80 kg, forevery 10 kg in excess of 80 kg of the patient's weight, an additional100 mL/hr is added. In yet another alternative embodiment, if there isurinary output, then the initial infusion rate is calculated using anequation based on the patient model.

FIG. 11A illustrates a modification to the method illustrated in FIG. 9that includes receiving the new infusion rate from the medical staff,1117. As discussed above in connection with FIG. 10A, the medical staffcan chose to ignore the recommendation of the decision-assist system ina semi-closed loop implementation or when the system is operating as adecision-assist system. When this occurs, the received infusion rate isused for calculating the new infusion rate the next time it iscalculated instead of using the previous recommended infusion rate.

Alternatively, the system can receive from the infusion pump the actualinfusion rate provided to the patient, 1122 as illustrated in FIG. 11B.The receiving of the actual infusion rate although illustrated asoccurring prior to obtaining the current urinary output, receiving ofthe actual infusion rate can occur at any point between calculations ofan infusion rate.

FIG. 12A illustrates a modification to the method illustrated in FIG. 9and its alternatives. The process covered by 1230 and 1235 can occur asillustrated after obtaining current urinary output 925, but this processcan occur before obtaining current urinary output 925 or before waitingfor a period of time 920. Analyzing the urinary output for problems,1030, such as erroneous or out of range urinary outputs. Examples ofproblems to analyze include low urinary output resulting from equipmentfailure, renal failure, inadequate perfusion of the kidneys typicallydue to low cardiac output or low renal perfusion, or the patient isotherwise non-responsive to the resuscitation. If a problem isdetermined to exist, notifying medical staff of the problem, 1035.Examples of the notification include, for example, sounding a visual oraudio alarm in the monitoring system connected to the patient includingbedside monitors and/or remote nurse's station monitoring equipment;sending an alarm notice to communication devices such as a pager,cellular telephone, or a telephone; sending an e-mail or text message todesignated recipients; and any combinations of these. The notificationin at least one embodiment includes a recommendation(s) as to how toproceed such as to check the equipment or consider inotropes. The typeof notification can be reflective of the problem or potential problemdetected. If the urinary output does not satisfy a problem condition(s),then calculate a new infusion rate, 920.

FIG. 12A also illustrates alternative processes to problem detection.Receiving an instruction in response to the notice sent in 1235 tomedical staff, 1240. Ending the process if the instruction is toterminate, 1245. Returning to the main process flow if the instructionis to proceed. In an alternative embodiment, the method includes settinga time limit to receiving the instruction in 1240 before proceeding withthe method if no instruction is received.

An alternative embodiment allows for the medical staff to terminate theprocess if the patient stabilizes during the resuscitation or a problemhas been detected independent of the method. When the patient hasstabilized, this is an indication that the resuscitation has beencompleted. An example of this is shown in FIG. 10D at the right arrow,where the net fluid level is shown as declining for a period of time,which is an indication that the inflammatory process after the burn isending as capillary leakage has been substantially repaired and thepatient is having adequate fluid retention at this point. One recognizeddefinition for the patient becoming stable is that urinary output isadequate with near maintenance level of fluid for three or more hours,and in some embodiments the time threshold is six hours when theresuscitation is between 24 and 48 hours. Another recognized definitionrequires that the patient has reached hemodynamic stability prior toresuscitation being ended. The system upon receiving such a notificationwould terminate and treat the notification like an interrupt. In atleast one embodiment, the system monitors the urinary output and theinfusion rate to determine whether the criteria for stability have beensatisfied for a period of time. In another embodiment, the systemreceives additional inputs regarding blood flow, blood pressure, andheart rate to allow for a determination to be made as to whetherhemodynamic stability has been obtained. An example of this is the meanarterial pressure 1040A being tracked by the system.

FIG. 12B illustrates an example of analyzing a couple of differenturinary output problems. Alternatively, different combinations thenthose illustrated could be used and these steps may be reordered. Asillustrated, the current urinary output (UO_(t)) is analyzed todetermine whether it is below an equipment failure threshold (UO_(ef)),1230A. The equipment failure threshold preferably is set at 5 mL/hr orits equivalent rate. However, the equipment failure threshold could beselected from a range of 0.5 mL/hr to 15 mL/hr. The equipment failurethreshold is set to allow for detection when there may be a problem withthe bladder catheter, for example, being blocked, kinked, removed, ordisconnected resulting in no or little urinary output. If this conditionis satisfied, then notifying the medical staff, 1235A, of the potentialproblem.

If the urinary output (UO_(t)) exceeds the equipment failure threshold(UO_(ef)), then determining whether the current output satisfiesnon-responsiveness criteria, 1230B, 1230C. If the non-responsivenesscriteria are satisfied, then notifying the medical staff, 1235B.Examples of non-responsiveness criteria include low current urinaryoutput and low urinary output for a predetermined amount of time.

Determining whether the urinary output (UO_(t)) is below a non-responsethreshold (UO_(nr)), 1230B, and when it is, then notifying the medicalstaff that the patient may be non-responsive and an intervention may berequired, 1235B. The non-response threshold (UO_(nr)) is illustrated inFIG. 12B, and may be, for example, 15 mL/hr. Alternatively, thisdetermination can also require that the current infusion rate be above acurrent infusion threshold that in at least one embodiment is dictatedby the hours post burn. An example is in Phase I the threshold is 500mL/hr, Phase II the threshold is 300 mL/hr, and Phase III the thresholdis 150 mL/hr.

If the urinary output (UO_(t)) is in excess of the non-responsethreshold (UO_(nr)), then determining whether the urinary output(UO_(t)) is below a target range (UO_(lt)) for a low time threshold,1230C. Alternatively, this determination can also require that thecurrent infusion rate be above a current infusion threshold asdiscussed, for example, in the paragraph above. If this determination ispositive, then notifying the medical staff that the patient may benon-responsive and an intervention may be required, 1235B.

As illustrated in FIG. 12C, the method in one embodiment includes aurinary output determination based on the urinary output (UO_(t))exceeding a target range (UO_(h)), 1230D. As discussed above indifferent examples, the high end of the target range (UO_(h)) may be 50mL/hr, but that this range can be adjusted based on current medicalapproaches. If the determination is positive, then setting the wait timeto a reduced period of time, 1240D instead of providing a notification,1235. Then determining a new infusion rate, 910. In another embodimentthe criteria to be satisfied in this determination includes that a hightime threshold is also satisfied, and in such a situation a notificationis provided to the medical staff, 1230.

An alternative embodiment when the problem embodiments are used is toinclude a check to see if the urinary output is within the target range,and if it is then to proceed to the calculation of the infusion rate,615.

Additional examples of problems or other triggers that can serve as abasis for alerting the medical staff in some embodiments includedifferent infusion rates being used for the first time or for a periodof time, size of the infusion rate change, cumulative infusion ratesexceed certain thresholds, projections exceed certain levels, and meanarterial pressure and other physiological conditions unrelated tourinary output. Examples of infusion rates used for the first timeinclude 125 mL/hr, 1000 mL/hr, and 2000 mL/hr. Examples of a change inthe infusion rate include greater than 30% of the previous infusion rateor 500 mL/hr. from the previous infusion rate. Another example of atrigger is if the average infusion rate exceeds 1000 mL/hr for sixhours. Examples of cumulative infusion rates exceeding certainthresholds include total volume greater than 200 mL/kg in 24 hours orless (in at least one embodiment accompanied by an early warning) and250 mL/kg in 24 hours or less (in at least one embodiment accompanied bya severed warning). An example of a projection is if the 12 hourcumulate volume will exceed 250 mL/kg. Examples of physiologicalconditions include urinary output less than 10 mL; mean arterialpressure less than 60 when urinary output is greater than 50 mL, and insuch a situation in at least one embodiment the recommended infusionrate will maintain the previous infusion rate in an attempt to increasethe mean arterial pressure; and sodium at hour 24 is less than 150,recommend continuation of LR and otherwise recommend to modify fluidbeing used. Other lab values or chemistry could be used such as whetherthe patient is acidotic (i.e., base deficient). Another potentialtrigger is that if the abdominal compartment pressure (measured forexample with sensor placed in the bladder via Foley catheter) hasincreased rapidly or exceeded a predetermined threshold, then alertingthe medical staff that the fluid therapy may need to be changed to avoidinjuries associated with over-resuscitation and to avoid the need tomake an incision into the abdomen.

In at least one embodiment after or before the wait period, the methodincludes a determination as to whether the patient has stabilized(although this determination could occur at any point in the method andact as an interrupt). FIG. 14 provides an example of this determination.The determination includes in at least one implementation receiving anotification from the medical staff that the patient has stabilized. Inanother implementation, the determination is made by the system based onphysiological readings for the patient. Both of these implementationscan be combined. Upon receiving a notice or determining the patient hasstabilized, terminating the resuscitation.

In at least one embodiment, the method further includes a variety oflimit checks when calculating the new infusion rate. Examples of limitchecks include infusion rate between 125 mL/hr and 2000 mL/hr, maximumchange of 500 mL/hr or a predetermined percentage such as ±20%, and nodecrease in infusion rate when mean arterial pressure is less than 60and urinary output is greater then the target range. In otherembodiments, the method recommends termination of the resuscitation when48 hours has elapsed in an ICU setting or 72 hours has elapsed in an PDAsetting, and the infusion rate has been at maintenance level (e.g., 125mL/hr or less) for a period of time (e.g., six hours between hours 24and 48). In at least one embodiment the system will run for at least thefirst 24 hours post burn before terminating.

Certain conditions have been shown to not necessarily work with theabove-described resuscitation method. The contraindications includeabnormal renal function, administration of diuretics (urinary outputwill be greater than normal), elevated blood alcohol level, severeelectrical injury, rhabdomyolysis requiring urinary output between 30and 50 mL/hr, acute MI, and cutaneous burns less than 20% TBSA. Evenwhen these conditions exist, the medical staff may still utilize theinvention in a resuscitation.

FIG. 13 illustrates an implementation example of the method usingdifferent aspects discussed above in connection with differentembodiments. Once the patient has been prepared to start theresuscitation including connection of an infusion line and a catheter tothe patient. The initial infusion rate is set for an infusion pump todeliver fluid to the patient, 1305. A period of time is allowed toelapse such as 10 minutes, 15 minutes, 30 minutes, or 60 minutesalthough over periods of time could be used in a range of 5 to 90minutes, 1310. Examples of how to maintain the wait delay include, forexample, a timer with or without an alarm that is displayed or notdisplayed for viewing by the medical staff. Alternatively, the waitdelay for the first time through the method may be shorter to provide aninitial urinary output and to allow for the infusion rate to be adjustedsooner to reflect the patient's condition. In at least one embodimentwhen the method is repeated again, the length of the delay is determinedbased on the current condition of the patient. Less frequent checks aredesirable to lessen the impact on the medical staff in terms ofmonitoring the patient, although the frequency should be at least oncean hour. However, if the output is sent to a closed-loop system, thenthe frequency will increase. The urinary output is obtained for theperiod of the wait delay to determine the flow rate in milliliters perhour, 1315.

The urinary output is compared to a predetermined range to see if itfalls within the range, 1320. The illustrated range is 30 mL/hr to 50mL/hr, which represents the current target range for urinary output foradults during resuscitation. One of ordinary skill in the art willappreciate based on this disclosure that this range may be adjustedbased on current thinking regarding the optimal urinary output or to beadapted for pediatric care. If the urinary output is in the desiredrange, then the wait delay is set for 1 hour, 1325. Although this waitperiod can be a variety of lengths as discussed above but given that theurinary output is in an acceptable range the wait delay can be longer tominimize the impact on staff resources. The infusion rate is calculated,1330, prior to setting the infusion rate, 1305.

However, if the urinary output is outside the range, then adetermination is made as to whether the urinary output is below thetarget range, 1335. Alternatively, the determination could be based onwhether the urinary output is above the target range and reversing theyes/no for the two branches leading to 1340 and 1380. This is anindication that the infusion rate needs to be adjusted potentiallyupwards to elevate the urinary output for the patient.

If the urinary output is low, then it is determined if the urinaryoutput is below a predetermined problem threshold, 1340. Thepredetermined problem threshold allows for the medical staff to benotified if the urinary output is such that there may have been a systemfailure or the patient has become non-responsive. The illustratedpredetermined problem threshold in FIG. 13 is 10 mL/hr, or as discussedabove in connection with FIG. 12B, this threshold could be 5 mL/hr. Ifthe urinary output is below the predetermined problem threshold, thenthe medical staff is alerted to a potential problem, 1345, to allow forthe medical staff to confirm that the system is working, for example,that the catheter has not been compromised, or that the patient isbecoming non-responsive and a new course of medical treatment may berequired. A termination decision is received from the medical staff onwhether the process should continue, 1350. If the termination decisionis yes, then the process is ended, 1355. If the termination decision isno, then the wait delay is set to a shorter period of time that is lessthan the regular wait delay to increase the frequency of the checks tospeed up the process of bringing the urinary output in the target range,for example, the illustrated wait delay is set to 30 minutes, 1360. Anew infusion rate is determined, 1365. FIGS. 5-8 provide examples of howthe new infusion rate may be determined.

If the urinary output is in excess of the predetermined threshold in1340, then it is determined how long the urinary output has been belowthe target range, 1370. The illustrated low output time threshold is twohours in 1370. There are a variety of ways that the length of time canbe determined including finding the last urinary output entry that wasin or above the target range and comparing the time stamp for that entryto the current time, starting a timer when the urinary output is belowthe target range, or starting a counter that is incremented based on thenumber of wait delay periods or fractions there of if shorten as occursin illustrated 1360. If the predetermined time threshold has beenexceeded, then the wait delay is set to a shorten period of time, 1360.If the time threshold has not been exceeded or met, then the wait delayis set for the regular length, which is illustrated as 1 hour in 1375.After the wait delay is set, then the next infusion rate is calculated,1365. In at least one embodiment, the processor starts a countdown timerthat will alarm when the timer reaches zero to alert the medical staffthat it is time to perform a check of the instruments. In anotherembodiment, at the end of the timer, the processor pulls (or receives)the necessary data from the infusion pump and urine meter. In yetanother embodiment implemented on a portable system with limited batterypower such as a PDA, the system hibernates (or other lowering of powerconsumption) between entry of at least one of the urinary output andinfusion rate information and normalizes the numbers to the requisitewait time for calculating the new infusion rate, 1365.

If in 1335, it is determined that the urinary output is not below thetarget range, then it is determined whether a high output time thresholdhas been exceeded, 1380. In FIG. 13, the high output time threshold isillustrated as 3 hours. As discussed above, there are a variety of waysthat can be used to track or determine the length of time. If the highoutput time threshold is not exceeded, then the wait delay is set for aregular wait time, which is illustrated as being 1 hour, 1385. If thehigh output time threshold has been exceeded, then the wait time is setfor a shorten length, which is illustrated as 30 minutes, 1390. A reasonfor a shorten time period for the wait length is to provide for morefrequent adjustment of the infusion rate to attempt to more rapidlybring the urinary output back into the urinary output target range.After the wait times are set, a new infusion rate is calculated, 1365,before repeating the process.

An alternative embodiment allows for the medical staff to terminate theprocess if the patient stabilizes during the resuscitation. The systemupon receiving such a notification would terminate and treat thenotification like an interrupt.

Another alternative embodiment would add an infusion rate condition tothe determinations associated with the problem threshold and low outputtime threshold. The condition would require that the infusion rate wasabove a current infusion threshold in addition to the other condition.The infusion rate could be time sensitive in that it decreases over theresuscitation period. An example of the decrease would be that for eachsixteen hour period the infusion rate would decrease. Examples for thecurrent infusion thresholds are 500 mL for the first twelve hours, 300mL for the next twenty-two hours, and 150 mL for the last fourteenhours. Although the infusion rate could be decreased linearly,exponentially or with any decay equation.

FIG. 14 illustrates another embodiment according to the invention forprovide decision support for conducting a resuscitation of a burnpatient. The method illustrated in FIG. 14 begins with receiving patientdata including an estimate of the burn size and approximate weight forthe patient, 1405. An additional parameter that may be received is thetime of the burn injury or the approximate number of hours since theburn injury. Based on the received parameters, calculating a TBSAmodifier (Y_(TBSA)) and a weight modifier (Y_(weight)), 1410.

The illustrated method then waits for a predetermined period of timebefore proceeding, 1415. The illustrated wait time is 1 hour although asdiscussed above other time lengths can be used. Alternatively, the waitdelay for the first time through the method may be shorter to provide aninitial urinary output and to allow for the infusion rate to be set toreflect the patient's condition. The urinary output is obtained, 1420.

The method in FIG. 14 further includes an error check relating to systemfailure or the patient being non-responsive to the resuscitation. Afterthe urinary output is measured, determining whether the urinary outputis below a problem threshold, 1421. The problem threshold is illustratedin FIG. 14 as being 5 mL/hr. If the urinary output is low, thennotifying the medical staff of the potential problem, 1422. Receivingfurther instructions from the medical staff regarding whether theresuscitation should continue, 1423. If the resuscitation is to end,then stopping the method, 1424. If the resuscitation is to continue,then measuring the urinary output again, 1420. If the urinary output isabove the problem threshold, then continuing to check the urinary outputagainst additional thresholds in FIG. 14.

A determination is made as to whether the urinary output is below anon-response threshold, 1425. The non-response threshold is illustratedin FIG. 14 as being 15 mL/hr. Alternatively, this determination can alsorequire that the current infusion rate be above a current infusionthreshold as discussed above. If this determination is positive, thennotifying the medical staff that the patient may be non-responsive andan intervention may be required, 1430. Receiving continuationinstructions from the medical staff, 1435. Proceeding based on thecontinuation instructions, 1440. If the continuation instructions are toend, then the process is ended, 1424. If the continuation instructionsare to proceed, then the new infusion rate is determined, 1450.

If the urinary output is in excess of the non-response threshold, thendetermining whether the urinary output is below a target range for a lowtime threshold, 1445. Alternatively, this determination can also requirethat the current infusion rate be above a current infusion threshold asdiscussed above. If this determination is positive, then notifying themedical staff that the patient may be non-responsive and an interventionmay be required, 1430. Receiving continuation instructions from themedical staff, 1435. Proceeding based on the continuation instructions,1440. If the continuation instructions are to end, then the process isended, 1424. If the continuation instructions are to proceed, then thenew infusion rate is determined, 1450.

If the urinary output is fine, then calculating a new infusion rate,1450. As discussed above, there are a variety of ways according to themethod for calculating an infusion rate. After the infusion rate iscalculated, then waiting for a predetermined time before repeating themethod, 1415. In at least one embodiment, the wait time is adjustedbased on whether certain urinary output conditions have been met. Forexample, if any of the urinary output determinations are positive, thenthe method can set the wait time to a shortened time period.

An alternative embodiment illustrated in FIG. 14 sets the initialinfusion rate for the resuscitation based on patient's weight and burnsize area. Recognized infusion equations include the Brooke and Parklandinfusion calculations in addition to the infusion equations discussedabove.

Also illustrated in FIG. 14 is an alternative embodiment that includes adetermination as to whether the patient has stabilized 1417 (althoughthis determination could occur at any point in the method and act as aninterrupt). The determination includes in at least one implementationreceiving a notification from the medical staff that the patient hasstabilized. In another implementation, the determination is made by thesystem based on physiological readings for the patient. Both of theseimplementations can be combined together. If the patient has stabilized,then ending the process, 1424.

FIG. 15A illustrates a system that is able to perform the differentmethods described above. The illustrated system includes a computer (orother processing device such as a personal data assistance, tablet PC)1505 with a display 1510 connected to an infusion pump 1515 such as anIV pump and a urinary output meter (or sensor) 1520 via serialconnectors and/or analog-to-digital convertors. Communication betweenthe different components of the system can occur through hardwire,wireless, or a combination. The computer 1505 can be continuouscommunication with the urinary output meter 1520 and/or the infusionpump 1515 collecting data for use in calculating new infusion rates.

The computer or other processing means 1505 will include a variety ofsoftware and firmware for performing the above-described methods and tocontrol the infusion pump according to the infusion rates determined bythe system or received from the medical staff. In particular asillustrated in FIG. 15B, the computer 1505 will include calculatingmeans 1506 for calculating an infusion rate in at least one of themanners described above, driving means 1507 for driving the display andreceiving user entered information via the display, and controllingmeans 1508 for controlling the operation of the infusion pump 1515. Inat least one embodiment, the computer 1505, the display 1510, andinfusion pump 1515 are integrally built together thereby increasing theportability of the system.

The system in at least one embodiment as illustrated in FIG. 15Cincludes a selector 1530 with at least two positions including a closedloop position and a semi-closed loop position that allows the user toselect how the system operates. The selector 1530 is in communicationwith said computer 1505. Examples of the selector 1530 include, forexample, a switch, slide device, a pair of push buttons, and a graphicalinterface element such as a virtual version of one of the mechanicalselectors. FIG. 15C also illustrates an alternative embodiment thatincludes a notification means for notifying the medical staff when aproblem has arisen, for example, with the system or the patient basedon, for example, a communication glitch in the system or physiologicaldata related to the patient has triggered a problem threshold asdiscussed above, for example, in connection with FIGS. 16A-16C.

In an implemented system, LabVIEW software is used for collection,management, control, and storage of digital, analog and multi-mediadata. Data retrieval and monitoring from instrumentation is stored in asynchronous fashion and can be monitored over a network (real time),stored in a database, retrieved for analysis as discrete digitalinformation or for waveform analysis, and played back in its originalcaptured form. In one implemented system, the system uses a FDA-approvedinfusion pumps (IMED Gemini PC-1, 2, 4) and a FDA-approved urine monitor(CritiCore, Bard Inc., Murray Hill, N.J.).

Automated fluid balance monitoring promotes an opportunity to generatedisplays of fluid balance, which in themselves may aid clinicians byrapidly imparting the time course of fluid balance. In at least oneembodiment, hourly (or other time period) data is recorded for infusionrates, urinary output and net volume to be displayed graphically toillustrate any relationships between fluid therapy and urinary outputfor a particular period. An example of this type of display is FIG. 10E,which is a screen capture showing cumulative fluid in 1015C, urinaryoutput 1020C, and net fluid (in minus urinary output) 1035C, measuredwith a prototype fluid balance monitor from data collected in an ovinemodel, consisting of 40% TBSA with acute respiratory distress syndrome(ARDS) secondary to inhalation injury. The display is generated from34,560 data points, infusion rate, and urinary volume measured every 10seconds for 48 hours. Per this experimental protocol, a steady infusionrate was set using the Parkland formula with adjustments only at 8- and24-hr post-injury time points. Clearly evident are periods of oliguria1020A at hours 28 through 35, despite continuous LR infusion at theParkland rate. Also observed, as indicated with arrows (⇓), are theresolutions of net fluid accumulation 1035C first occurring transientlyat 6-12 hours and then after 36 hours.

Another implemented version of a decision assist system uses manualhourly data input and provides hourly recommendations of infusion rate.One version of this system is built for tablet PCs for bedside use.Another version is written in JAVA code for implementation on USAISRstandard clinical monitors. A mobile implementation of the software waswritten for use on a personal digital assistant (PDA) or smart phonethat is field deployable and can be used in austere environments. Themethod can be implemented using a variety of software packages and/orcomputer languages.

FIGS. 10A and 10B show two displays of the pocket PC fluid balancemonitor with decision assist running. FIG. 10A illustrates a screenshotdisplaying infusion rates 1025A and urinary output 1020A for differenthours during resuscitation with the recommended infusion rate 1005Abeing represented by the dots. The display in at least one embodimentwill color code the urinary output to use one color to represent urinaryoutput in range and one or more colors for when the urinary output isoutside the target range. FIG. 10A illustrates an interface example forthe medical staff to provide the infusion rate 1010 when the recommendedinfusion rate 1005 is changed and the urinary output and in response tothe urinary output 1020 receive a recommendation for the infusion rate1005 for the next time period. FIGS. 16A-16E illustrate differentinterface examples associated with FIGS. 10A and 10B that share a commontab arrangement for viewing different aspects and views of datacollected by the system. FIG. 16A illustrates a data display screen thatis illustrated as including hours post burn, infusion rate, DSS, urinaryoutput (UO), cumulative infusion amount (Tin), and cumulative urinaryoutput (TUO). The interface illustrated in FIG. 16A also allows the userto scroll 1605 through the data to look at desired data for particularhours and to add new data 1610. FIG. 16B illustrates an interfaceexample for showing actual infusion rate (the bar graph) 1015A andrecommend infusion rate (dots) 1005A versus time. FIG. 16C illustratesan interface example for showing urinary output 1020A versus time with asuperimposed target range 1030. FIG. 16D illustrates an interfaceexample for showing total infusion volume 1015C at each hour post burn,while FIG. 16E illustrates an interface example for showing totalurinary output volume 1020C at each hour post burn.

FIG. 17 illustrates another interface example for use in a manual dataentry implementation. The illustrated interface includes identificationof the patient 1705, the patient's weight 1710, the last sampling period1715, the infusion rate 1720, the urinary output in volume 1725 andconverted to mL/kg 1730, identification of the next sampling period1735, and a display area 1740. Both the infusion rate and urine outinclude arrow keys that can be used to adjust the value in therespective field if necessary. The display area 1740 can be used todisplay a variety of information as discussed above in connection withother figures even though the hourly urinary output is illustrated. Theinterface also includes an icon 1745 for obtaining the new infusion rateonce the information for the last sampling period has been entered intothe system. In an alternative embodiment, the icon 1745 could instead beused to accept the recommended infusion rate. The recommended infusionrate 1750 is display. The illustrated interface also includes examplesof different warnings and alerts that can be provided including oiguria1755, anuria 1760, recommendations of things to check 1765, and currentstatus 1770. In at least one embodiment, the oiguria and anuria areaschange color and/or brightness to indicate when those conditions exist.

The invention in at least one embodiment includes mechanisms forhandling errors that may arise during use of the system. The system inat least one embodiment includes a robust data collection function withcontinuous data capture and display generation for 48 hours in severalanimal studies and up to 57 hours in patients. One main source of errorsthat can arise is when cables are disconnected or the urine monitor isnot level. Errors generated by the system are classified into permanentor recoverable. Permanent errors entail the shutting off andre-initialization of the system. Recoverable errors are reported to thecaregiver and logged by the system. In this case, the physician willdecide whether to restart the system or to continue normal operationwhen recovered. A system of clinical alarms provides details to assistthe caregiver in deciding when to disengage the system and initiatemanual pump control. Error reduction algorithms can autocorrect for avariety of errors. For example, if the Bard urine collection canister isshaken, incorrect data changes in urine volume are transiently sent tothe computer. Computer-generated alarms, notes, or comments aredocumented in the data record log and provided to the caregiver by popupwindows. The current closed loop system version searches for devices toregain device connectivity. For example, when the connection is lost tothe pump or urine monitor, an alarm and popup notifies the caregiverthat the connection is lost. When the caregiver reattaches theconnection, the data collection and algorithm resume. If either pump orurinary connectivity is lost for greater than five minutes an alarmnotifies the caregiver to assume manual control and to restart theprogram manually.

When errors with connections arise, then in at least one embodiment, thesystems will become decision-assist systems that allow for data to bemanually entered by the medical staff and the system will provided arecommended infusion rate and other information as described above.

Research findings support that at least one embodiment of this inventionwill assist with resuscitation during the first 48 hours includingproviding fluid infusion recommendations based on a review of 30 burnpatients admitted to the burn ICU at the U.S. Army Institute of SurgicalResearch burn unit and the University of Texas Medical Branch burn ICU.

Patients with at least 20 percent total body surface area (TBSA) burnwere considered for this study. Patients with electrical burns or whowere intoxicated were excluded from this study. Fluid was initiatedbased on the standard Brooke (2 ml/kg/% TBSA over 24 hours) or Parkland(4 ml/kg/% TBSA over 24 hours) resuscitation formulas. Mean percentageof total body surface area was 39.8±21.4%. Mean age was 40±21 years.Infusion rate model was fitted using a decaying exponential curve asillustrated in FIG. 19. Mean expected urinary output or the first 48hours is shown in FIG. 20. Based on mean urinary output values, onaverage patients are severely over resuscitated a majority of the time.The non-linear relationship between the infusion and urinary output wasmitigated by subdividing the decaying curve into 3 distinct phasesrepresenting initial, middle, and end infusion phases illustrated inFIG. 21. In the initial phase (postburn hour 0-13) there is substantialvariability between infusion rates and urinary outputs. Phase II(postburn hour 13-34) and phase III (postburn hour 34-48) algorithms aresimilarly designed and found to be sequentially less aggressive.Algorithm models an average infusion drop of 36 ml/hr for the first 13hours, 23 ml/hr for hours 13 to 33, and 11 ml/hr for hours 33 to 48 witha corresponding urinary output increase of 1.2 ml/hr for all 48 hrs.Infusion requirements were then calculated using equation (1A):

$\begin{matrix}{I_{t} = {I_{t - 1} + {{e(t)} \times \frac{I\; R\; C_{t}}{{UOC}_{t}}}}} & \left( {1A} \right)\end{matrix}$FIG. 22 illustrates the expected algorithm recommendations compared tothe mean model values. Estimated algorithm recommendations resulted in atotal fluid infusion of 55% below actual values for achieving anappropriate urinary output target.

The invention can take the form of an entirely hardware embodiment or anembodiment containing both hardware and software elements. In at leastone exemplary embodiment, the invention is implemented in a systemrunning software, which includes but is not limited to firmware,resident software, microcode, etc.

Furthermore, the invention can take the form of a computer programproduct accessible from a computer-usable or computer-readable mediumproviding program code for use by or in connection with a computer orany instruction execution system. For the purposes of this description,a computer-usable or computer readable medium can be any apparatus thatcan contain, store, communicate, propagate, or transport the program foruse by or in connection with the instruction execution system,apparatus, or device.

The medium can be an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system (or apparatus or device) or apropagation medium such as carrier signal. Examples of acomputer-readable medium include a semiconductor or solid state memory,magnetic tape, a removable computer diskette, a random access memory(RAM), a read-only memory (ROM), a rigid magnetic disk, and an opticaldisk. Current examples of optical disks include compact disk-read onlymemory (CD-ROM), compact disk-read/write (CD-R/W) and DVD.

A data processing system suitable for storing and/or executing programcode will include at least one processor coupled directly or indirectlyto memory elements through a system bus. The memory elements can includelocal memory employed during actual execution of the program code, bulkstorage, and cache memories which provide temporary storage of at leastsome program code in order to reduce the number of times code must beretrieved from bulk storage during execution.

Network adapters may also be coupled to the system to enable the dataprocessing system to become coupled to other data processing systems orremote printers or storage devices through intervening private or publicnetworks. Modems, cable modem and Ethernet cards are just a few of thecurrently available types of network adapters.

Computer program code for carrying out operations of the presentinvention may be written in a variety of computer programming languages.The program code may be executed entirely on at least one computingdevice, as a stand-alone software package, or it may be executed partlyon one computing device and partly on a remote computer. In the latterscenario, the remote computer may be connected directly to the onecomputing device via a LAN or a WAN (for example, Intranet), or theconnection may be made indirectly through an external computer (forexample, through the Internet, a secure network, a sneaker net, or somecombination of these).

It will be understood that each block of the flowchart illustrations andblock diagrams and combinations of those blocks can be implemented bycomputer program instructions and/or means. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing the functionsspecified in the flowcharts or block diagrams.

The exemplary and alternative embodiments described above may becombined in a variety of ways with each other. Furthermore, the stepsand number of the various steps illustrated in the figures may beadjusted from that shown.

It should be noted that the present invention may, however, be embodiedin many different forms and should not be construed as limited to theembodiments set forth herein; rather, the embodiments set forth hereinare provided so that the disclosure will be thorough and complete, andwill fully convey the scope of the invention to those skilled in theart. The accompanying drawings illustrate exemplary embodiments of theinvention.

Although the present invention has been described in terms of particularexemplary and alternative embodiments, it is not limited to thoseembodiments. Alternative embodiments, examples, and modifications whichwould still be encompassed by the invention may be made by those skilledin the art, particularly in light of the foregoing teachings.

As used above “substantially,” “generally,” and other words of degreeare relative modifiers intended to indicate permissible variation fromthe characteristic so modified. It is not intended to be limited to theabsolute value or characteristic which it modifies but rather possessingmore of the physical or functional characteristic than its opposite, andpreferably, approaching or approximating such a physical or functionalcharacteristic.

Those skilled in the art will appreciate that various adaptations andmodifications of the exemplary and alternative embodiments describedabove can be configured without departing from the scope and spirit ofthe invention. Therefore, it is to be understood that, within the scopeof the appended claims, the invention may be practiced other than asspecifically described herein.

VI. INDUSTRIAL APPLICABILITY

The invention has industrial applicability to assist in theresuscitation of injured individuals who have received burns. Theinvention brings expertise out of the expert burn centers to medicalstaffs that may have no expertise and thus the care level provided bythose medical staffs to patients should improve. The semi-closed loopsystem and the closed loop system are both useable in caring for burnpatients when the medical staff does not have a sufficient level ofexperience and/or background to care for the burn patient, particularlyduring transport to a burn center.

VII. GLOSSARY

ABA—American Burn Association

ABLS—Advanced Burn Life Support

HPB—Hours Post Burn

LR—lactated Ringer's solution

PID—proportional-integral-derivative

TBSA—Total Body Surface Area

% TBSA—percentage Total body surface area

UO—Urinary Output

USAISR—U.S. Army Institute of Surgical Research

UTMB—University of Texas Medical Branch

We claim:
 1. A system for use in resuscitating a patient comprising: aurine sensor; an infusion pump; and a processor connected to said urinesensor and said infusion pump, said processor having means forcalculating an infusion rate using an infusion rate model based on atleast a current infusion rate, a current urinary output, and infusionrate model based constants, the new infusion rate is calculated usingthe following equation$I_{t} = {I_{t - 1} + {{e(t)} \times \frac{I\; R\; C_{t}}{{UOC}_{t}}}}$where I_(t) is the new infusion rate, I_(t-1) is the last infusion rate,e(t) is the urinary output error between the current urinary output anda target urinary output, IRC_(t) is the infusion rate constant at time tbased on the hours post burn, and UOC_(t) is the urinary constant, andmeans for controlling operation of said infusion pump based on thecalculated infusion rate.
 2. The system according to claim 1, whereinthe infusion rate constant decreases based on hours post-burn in atleast two steps.
 3. The system according to claim 1, wherein the urinaryoutput error is further multiplied by at least one of a modifier basedon a patient's weight, a modifier based on a percentage of a total bodysurface area burned, and a Gaussian function calculated using an endpoint of a target urinary output range furthest from the current urinaryoutput.
 4. The system according to claim 1, wherein the urinary outputerror is further multiplied by a Gaussian function calculated using anend point of a target urinary output range furthest from the currenturinary output, where the Gaussian function is calculated usingG=1−Ae ^(−(X−B)) ² ^(/C) ² where A is set to 1; X is set to the currenturinary output; B is set to the furthest end point of the target urinaryoutput range; and C is set to
 5. 5. The system according to claim 1,further comprising a timer connected to said processor, said calculatingmeans calculates a new infusion rate when said timer expires afterrunning for a predetermined time.
 6. The system according to claim 5,wherein the predetermined time is based on hours post burn.
 7. Thesystem according to claim 1, further comprising a display, and saidprocessor further includes means for driving said display and receivinginformation from said display of information entered by a user includingan infusion rate different than the infusion rate calculated, and saidcontrolling means operates the infusion pump at the different infusionrate received from the user until a new infusion rate is received orcalculated.
 8. The system according to claim 1, further comprising aselector with at least two positions including a closed loop positionand a semi-closed loop position, said selector is in communication withsaid processor.
 9. The system according to claim 1, further comprisingmeans for notifying medical staff when a problem has arisen with thepatient.
 10. The system according to claim 1, further comprising meansfor notifying medical staff when a problem has arisen with the system.11. The system according to claim 1, wherein said urine sensor includesa drop rate sensor.
 12. A system for use in resuscitating a patientcomprising: a urine sensor; an infusion pump; a timer; and a processorconnected to said urine sensor, said infusion pump, and said timer, saidprocessor having means for calculating an infusion rate in response to asignal from said timer and based on at least the current infusion rate,the current urinary output, infusion rate model based constants, thepatient's weight, the percentage of total body surface area, and aGaussian function centered on a target urinary output, and means forcontrolling operation of said infusion pump based on the calculatedinfusion rate.
 13. The system according to claim 12, wherein theinfusion rate model based constants include an infusion rate constantand a urinary output constant.
 14. The system according to claim 12,further comprising a display, and said processor further includes meansfor driving said display and receiving information from said display ofinformation entered by a user including an infusion rate different thanthe infusion rate calculated, and said controlling means operates theinfusion pump at the different infusion rate received from the useruntil a new infusion rate is received or calculated.
 15. The systemaccording to claim 12, further comprising a selector with at least twopositions including a closed loop position and a semi-closed loopposition, said selector is in communication with said processor.
 16. Thesystem according to claim 12, wherein said calculating means uses thefollowing equation$I_{t} = {I_{t - 1} + {{e(t)} \times \frac{I\; R\; C_{t}}{{UOC}_{t}} \times Y_{weight} \times Y_{tbsa} \times G_{UO}}}$where I_(t) is the new infusion rate, I_(t-1) is the last infusion rate,e(t) is the urinary output error, IRC_(t) is the infusion rate constantat time t based on the hours post burn, UOC_(t) is the urinary constant,Y_(weight) is a modifier based on the patient's weight, Y_(tbsa) is amodifier based on the percentage of the total body surface area, andG_(UO) is the Gaussian function based on the target urinary output. 17.The system according to claim 16, wherein the Gaussian function iscalculated using an end point of a target urinary output range furthestfrom the current urinary output, where the Gaussian function iscalculated usingG=1−Ae ^(−(X−B)) ² ^(/C) ² where A is set to 1; X is set to the currenturinary output; B is set to the furthest end point of the target urinaryoutput range; and C is set to
 5. 18. The system according to claim 12,further comprising means for notifying medical staff when a problem hasarisen with at least one of the patient and the system.
 19. A system foruse in resuscitating a patient comprising: a urine sensor; an infusionpump; receiving means for receiving patient data including percentage oftotal body surface area burned and time since the patient was burned;first means for calculating an initial infusion rate based on at leastthe received patient data; second means for calculating an urinaryoutput error based on a difference between a target urinary output and acurrent urinary output provided by said urine sensor; third means forcalculating a new infusion rate based on at least the calculated urinaryoutput error multiplied by a constant calculated in part based on anexponential function with the input of hours post burn for the patientwith the result being added to the current infusion rate; outputtingmeans for outputting the new infusion rate to said infusion pump; and atimer for controlling the operation of said second means, said thirdmeans and said outputting means.
 20. The system according to claim 19,further comprising a processor having said receiving means, said firstmeans, said second means, said third means, and said outputting means.